File name changes during "save as" to other directory

Recently I noticed that whenever I get a document in my email, or a file
that I'm downloading, and I want to save it to a specific area, the name of
the file suddenly changes to a name that is already in the directory. My
"save as name" is not what I started out with. If I leave the area that the
MS defaults to alone, it keeps the same name though. This only happens if I
pick a different area to save in. What is going on????? I never had that
problem before.